The present invention relates to a fault diagnosis technique by which fault diagnosis of a photovoltaic (PV) module is performed in a PV power system constituted of multiple PV cell modules.
Examples of techniques for fault diagnosis of a PV power system are disclosed in JP 2012-114108 A (Patent Document 1), JP 2012-54401 A (Patent Document 2), and JP 2014-45073 A (Patent Document 3).
Patent Document 1 discloses the following: “the power generation amounts are acquired and stored, the power generation amounts for an evaluation time of a sampling period are calculated, the greatest power generation amounts therein are extracted, and the average thereof is set as a reference value. Also, the power generation amounts during the evaluation time of an evaluation period are calculated, the greatest power generation amounts therein are extracted, and the average thereof is set as an evaluation value. Whether or not there is a fault in the system is determined on the basis of the difference between the reference value and the evaluation value.”
Patent Document 2 discloses the following: “power generation information, solar radiation information, and temperature information are acquired, such information is stored, and a system output coefficient during a diagnostic period is calculated and stored along with the temperature during the diagnostic period. A prediction formula is derived from the system output coefficient prior to the day during which diagnosis is to be performed, and using this prediction formula, a predicted system output coefficient is calculated from the temperature during the diagnostic period on the day during which diagnosis is to be performed. The system output coefficient on the day during which diagnosis is to be performed is read in as an actual system output coefficient. When the difference between the predicted system output coefficient and the actual system output coefficient is at or above a certain amount, a fault is diagnosed in the photovoltaic power system and this diagnosis is displayed.”
Patent Document 3 discloses the following: “while updating a prescribed coefficient that is the ratio of a short-circuit current to an operating current, according to the photovoltaic cell array state, the solar radiation amount is calculated, and measurement data including an operating current and operating voltage measured by a detection unit is used, thereby calculating an operating temperature and a fault value of a photovoltaic cell module in the photovoltaic cell array.”